U.S. patent application number 13/444956 was filed with the patent office on 2013-10-17 for systems and apparatus relating to reheat combustion turbine engines with exhaust gas recirculation.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is Stanley Frank Simpson, Lisa Anne Wichmann. Invention is credited to Stanley Frank Simpson, Lisa Anne Wichmann.
Application Number | 20130269310 13/444956 |
Document ID | / |
Family ID | 48095595 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130269310 |
Kind Code |
A1 |
Wichmann; Lisa Anne ; et
al. |
October 17, 2013 |
SYSTEMS AND APPARATUS RELATING TO REHEAT COMBUSTION TURBINE ENGINES
WITH EXHAUST GAS RECIRCULATION
Abstract
A power plant configured to include a recirculation loop about
which a working fluid is recirculated. The recirculation loop may
include a plurality of components configured to accept an outflow
of working fluid from a neighboring upstream component and provide
an inflow of working fluid to a neighboring downstream component.
The recirculation loop may include: a recirculation compressor; an
upstream combustor; a high-pressure turbine; a downstream
combustor; a low-pressure turbine; and a recirculation conduit
configured to direct the outflow of working fluid from the
low-pressure turbine to the recirculation compressor. The power
plant further may include: an oxidant compressor configured to
provide compressed oxidant to one of the upstream combustor and the
downstream combustor; and means for extracting a portion of the
working fluid from an extraction point disposed at a predetermined
location on the recirculation loop.
Inventors: |
Wichmann; Lisa Anne;
(Simpsonville, SC) ; Simpson; Stanley Frank;
(Simpsonville, SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wichmann; Lisa Anne
Simpson; Stanley Frank |
Simpsonville
Simpsonville |
SC
SC |
US
US |
|
|
Assignee: |
General Electric Company
|
Family ID: |
48095595 |
Appl. No.: |
13/444956 |
Filed: |
April 12, 2012 |
Current U.S.
Class: |
60/39.52 ;
60/39.5; 60/726; 60/746 |
Current CPC
Class: |
F02C 3/34 20130101 |
Class at
Publication: |
60/39.52 ;
60/726; 60/39.5; 60/746 |
International
Class: |
F02C 3/34 20060101
F02C003/34; F02C 6/10 20060101 F02C006/10; F02C 7/228 20060101
F02C007/228; F02C 3/04 20060101 F02C003/04 |
Claims
1. A power plant configured to include a recirculation loop about
which a working fluid is recirculated, the recirculation loop
comprising a plurality of components configured to accept an
outflow of working fluid from a neighboring upstream component and
provide an inflow of working fluid to a neighboring downstream
component, wherein the recirculation loop includes: a recirculation
compressor; an upstream combustor positioned downstream of the
recirculation compressor; a high-pressure turbine positioned
downstream of the upstream combustor; a downstream combustor
positioned downstream of the high-pressure turbine; a low-pressure
turbine positioned downstream of the downstream combustor; and a
recirculation conduit configured to direct the outflow of working
fluid from the low-pressure turbine to the recirculation
compressor, the power plant comprising: an oxidant compressor
configured to provide compressed oxidant to one of the upstream
combustor and the downstream combustor; and means for extracting a
portion of the working fluid from an extraction point disposed at a
predetermined location on the recirculation loop.
2. The power plant according to claim 1, wherein: the outflow of
working fluid from the low-pressure turbine comprises exhaust
gases, which, via the recirculation conduit, are directed to the
recirculation compressor; the recirculation compressor is
configured to compress the exhaust gases such that the outflow of
working fluid from the recirculation compressor comprises
compressed exhaust gases; and the means for extracting the portion
of the working fluid from the extraction point includes means for
controlling an extracted working fluid amount that is extracted at
the extraction point.
3. The power plant according to claim 2, wherein the recirculation
conduit is configured to collect the portion of the exhaust gases
from the low-pressure turbine and direct the portion of the exhaust
gases through a stretch of conduit such that the exhaust gases are
supplied to an intake of the recirculation compressor; wherein the
recirculation conduit further comprises a heat recovery steam
generator, the heat recovery steam generator including a boiler;
and wherein the heat recovery steam generator is configured such
that the exhaust gases from the low-pressure turbine comprises a
heat source for the boiler.
4. The power plant according to claim 2, wherein at least one of a
chiller and a blower are positioned on the recirculation conduit;
wherein the chiller comprises means for controllably removing an
amount of heat from the exhaust gases flowing through the
recirculation conduit such that a more desirable temperature is
achieved at the intake of the recirculation compressor; and wherein
the blower comprises means for controllably circulating the exhaust
gases flowing through the recirculation conduit such that a more
desirable pressure is achieved at the intake of the recirculation
compressor.
5. The power plant according to claim 2, further comprising an
upstream combustor fuel supply and a downstream combustor fuel
supply; wherein: the upstream combustor fuel supply includes means
for controllably varying a fuel amount supplied to the upstream
combustor; and the downstream combustor fuel supply includes means
for controllably varying a fuel amount supplied to the downstream
combustor.
6. The power plant according to claim 5, further comprising an
oxidant conduit configured to channel the compressed oxidant from
the oxidant compressor to the one of the upstream combustor and the
downstream combustor; wherein the oxidant conduit comprising means
for controllably varying a compressed oxidant amount supplied to
the one of the upstream combustor and the downstream combustor.
7. The power plant according to claim 6, wherein the oxidant
conduit further comprises means for delivering the compressed
oxidant to the one of the upstream combustor and the downstream
combustor at a preferable injection pressure level.
8. The power plant according to claim 7, wherein the means for
delivering the compressed oxidant to the one of the upstream
combustor and the downstream combustor at the preferable injection
pressure level comprises a chosen extraction location on the
oxidant compressor from which compressed oxidant at a desirable
pressure is extracted.
9. The power plant according to claim 7, further comprising a
booster compressor disposed on the oxidant conduit and an oxidant
valve that comprises the means for controllably varying the
compressed oxidant amount supplied to the one of the upstream
combustor and the downstream combustor; wherein the booster
compressor is configured to boost the pressure of the compressed
oxidant flowing through the oxidant conduit such that the
compressed oxidant supplied to the one of the upstream combustor
and the downstream combustor corresponds to a preferable injection
pressure level.
10. The power plant according to claim 9, further comprising an
atmosphere vent disposed on the oxidant conduit between the oxidant
compressor and the booster compressor, the atmosphere vent
configured to controllably vary a compressed oxidant amount vented
to the atmosphere.
11. The power plant according to claim 6, further comprising means
for controlling the power plant such that one of the upstream
combustor and the downstream combustor operates at a preferred
stoichiometric ratio; wherein the predetermined location of the
extraction point comprises a range of positions on the
recirculation loop, the range of positions being defined between
whichever of the upstream combustor and the downstream combustor is
operable at the preferred stoichiometric ratio and, proceeding in a
downstream direction, the other of the upstream and downstream
combustor.
12. The power plant according to claim 11, wherein: if the oxidant
compressor is configured to provide compressed oxidant to the
upstream combustor, the power plant includes means for controlling
the downstream combustor to operate at the preferred stoichiometric
ratio; and if the oxidant compressor is configured to provide
compressed oxidant to the downstream combustor, the power plant
includes means for controlling the upstream combustor to operate at
the preferred stoichiometric ratio.
13. The power plant according to claim 11, wherein the means for
controlling the power plant such that one of the upstream combustor
and the downstream combustor operates at the preferred
stoichiometric ratio includes a computerized control unit that is
configured to control the operation of the following components:
the means for controllably varying the compressed oxidant amount
supplied to the one of the upstream combustor and the downstream
combustor; the means for controllably varying the fuel amount
supplied to the upstream combustor; and the means for controllably
varying the fuel amount supplied to the downstream combustor; and
wherein the preferred stoichiometric ratio is a stoichiometric
ratio near 1.
14. The power plant according to claim 13, wherein the preferred
stoichiometric ratio comprises a stoichiometric ratio of between
0.75 and 1.25.
15. The power plant according to claim 13, wherein the preferred
stoichiometric ratio comprises a stoichiometric ratio of between
0.9 and 1.1.
16. The power plant according to claim 13, wherein the preferred
stoichiometric ratio comprises a stoichiometric ratio of between
1.0 and 1.1.
17. The power plant according to claim 11, wherein the oxidant
compressor is configured to provide compressed oxidant to the
upstream combustor but not the downstream combustor; and wherein
the means for controlling the power plant such that one of the
upstream combustor and the downstream combustor operates at the
preferred stoichiometric ratio comprises means for controlling the
power plant such that the downstream combustor operates at the
preferred stoichiometric ratio.
18. The power plant according to claim 17, wherein the
predetermined location of the extraction point comprises a range of
positions on the recirculation loop, the range of positions being
defined between the downstream combustor and, proceeding in a
downstream direction, the upstream combustor.
19. The power plant according to claim 18, wherein: the upstream
combustor is configured to combine the compressed oxidant from the
oxidant compressor with the compressed exhaust gases from the
recirculation compressor and, there within, combust the fuel from
the upstream combustor fuel supply; and the downstream combustor is
configured to operate without a supply of compressed oxidant
supplied directly from a compressor, the downstream combustor being
configured to combust the fuel from the downstream combustor fuel
supply with an excess oxidant in the exhaust gases from the
high-pressure turbine.
20. The power plant according to claim 18, further comprising means
for testing the working fluid to determine whether the downstream
combustor is operating at the preferred stoichiometric ratio;
wherein the means for testing the working fluid is positioned on
the recirculation loop relative to the predetermined position of
the extraction point.
21. The power plant according to claim 20, the means for testing
the working fluid comprises at least one of a sensor for detecting
excess oxidant and a sensor for detecting unspent fuel; and wherein
the position of the means for testing the working fluid on the
recirculation loop comprises a range of positions, the range of
positions being defined between the extraction point and,
proceeding in an upstream direction, the downstream combustor.
22. The power plant according to claim 11, wherein the oxidant
compressor is configured to provide compressed oxidant to the
downstream combustor but not the upstream combustor; and wherein
the means for controlling the power plant such that one of the
upstream combustor and the downstream combustor operates at the
preferred stoichiometric ratio comprises means for controlling the
power plant such that the upstream combustor operates at the
preferred stoichiometric ratio.
23. The power plant according to claim 22, wherein the
predetermined location of the extraction point comprises a range of
positions on the recirculation loop, the range of positions being
defined between the upstream combustor and, proceeding in a
downstream direction, the downstream combustor.
24. The power plant according to claim 23, wherein: the downstream
combustor is configured to combine the compressed oxidant from the
oxidant compressor with the exhaust gases from the high-pressure
turbine and, there within, combust the fuel from the downstream
combustor fuel supply; and the upstream combustor is configured to
operate without a supply of compressed oxidant supplied directly
from any compressor, the upstream combustor being configured to
combust the fuel from the upstream combustor fuel supply within an
excess oxidant contained in the flow of compressed exhaust from the
recirculation compressor.
25. The power plant according to claim 23, further comprising means
for testing the working fluid to determine whether the upstream
combustor is operating at the preferred stoichiometric ratio;
wherein the means for testing the working fluid is positioned on
the recirculation loop relative to the predetermined position of
the extraction point.
26. The power plant according to claim 25, the means for testing
the working fluid comprises at least one of a sensor for detecting
excess oxidant and a sensor for detecting unspent fuel; and wherein
the position of the means for testing the working fluid on the
recirculation loop comprises a range of positions, the range of
positions being defined between the extraction point and,
proceeding in an upstream direction, the upstream combustor.
27. The power plant according to claim 13, further comprising an
oxygen sensor configured to test the working fluid of the
recirculation loop, the oxygen sensor disposed between the
extraction point and, proceeding in an upstream direction on the
recirculation loop, the first of the upstream combustor and the
downstream combustor encountered; further comprising means for
determining whether the oxygen content exceeds a predetermined
threshold.
28. The power plant according to claim 20, wherein the
predetermined location for the extraction point comprises a
position just upstream of the upstream combustor; and wherein the
means for testing the working fluid comprises an oxygen sensor that
is disposed just upstream of the extraction point.
29. The power plant according to claim 2, further comprising: a
load; and a common shaft that connects the load, the oxidant
compressor, the recirculation compressor, the high-pressure turbine
and the low-pressure turbine such that the high-pressure turbine
and the low-pressure turbine drive the load, the oxidant
compressor, and the recirculation compressor.
30. The power plant according to claim 29, wherein: the load
comprises a generator; on the common shaft, the recirculation
compressor resides between the high-pressure turbine and the
oxidant compressor; and wherein, on the common shaft, the
high-pressure turbine resides between the low-pressure turbine and
the recirculation compressor.
31. The power plant according to claim 2, further comprising: a
generator; and concentric shafts including a first shaft and a
second shaft; wherein the first shaft connects to the high-pressure
turbine and drives at least one of the generator, the oxidant
compressor, and the recirculation compressor; and wherein the
second shaft connects to the low-pressure turbine and drives at
least one of the generator, the oxidant compressor, and the
recirculation compressor.
32. The power plant according to claim 2, wherein the means of
extracting a portion of the working fluid comprises an extraction
valve that is configured to controllably vary the portion of the
working fluid extracted.
33. The power plant according to claim 2, wherein the recirculation
conduit comprises means for controllably venting a portion of the
working fluid to atmosphere.
Description
BACKGROUND OF THE INVENTION
[0001] This application is related to [GE Docket 249104], [GE
Docket 250883], [GE Docket 250884], [GE Docket 250998], [GE Docket
254241], [GE Docket 256159], [GE Docket 257411], and [GE Docket
258552] filed concurrently herewith, which are fully incorporated
by reference herein and made a part hereof.
[0002] This present application relates generally to combustion
turbine engines and systems related thereto. More specifically, but
not by way of limitation, the present application relates to
methods, systems and/or apparatus for achieving operation at the
stoichiometric point and extracting a working fluid having desired
characteristics within various types of combustion turbine systems
having exhaust gas recirculation.
[0003] Oxidant-fuel ratio is the mass ratio of oxidant, typically
air, to fuel present in an internal combustion engine. As one of
ordinary skill in the art will appreciate, if just enough oxidant
is provided to completely burn all of the fuel, a stoichiometric
ratio of 1 is achieved (which may be referred to herein as
"operating at the stoichiometric point" or "stoichiometric point
operation"). In combustion turbine systems, it will be appreciated
that combustion at the stoichiometric point may be desirable for
several reasons, including lowering emissions levels as well as
performance tuning reasons. In addition, by definition,
stoichiometric point operation may be used to provide an exhaust
(which, in the case of a system that includes exhaust
recirculation, may be referred to generally as "working fluid")
that is substantially free of oxygen and unspent fuel. More
specifically, when operating at the stoichiometric point, the
working fluid flowing through certain sections of the recirculation
circuit or loop may consists of significantly high levels of carbon
dioxide and nitrogen, which, when fed into an air separation unit,
may yield substantially pure streams of these gases.
[0004] As one of ordinary skill in the art will appreciate,
producing gas streams of carbon dioxide and nitrogen in this manner
has economic value. For example, the sequestration of carbon
dioxide has potential value given current environmental concerns
relating to emission of this gas. In addition, pure gas streams of
carbon dioxide and nitrogen are useful in many industrial
applications. Also, carbon dioxide may be injected into the ground
for enhanced oil recovery. As a result, novel power plant system
configurations and/or control methods that provide efficient
methods by which stoichiometric point operation may be achieved
would be useful and valuable. This would be particularly true if
novel systems and methods provided effective ways by which existing
power plants using reheat and exhaust gas recirculation could
achieve improved operation via relatively minor, cost-effective
modifications. Other advantages to the systems and methods of the
present invention will become apparent to one of ordinary skill in
the art given the description of several exemplary embodiments that
is provided below.
BRIEF DESCRIPTION OF THE INVENTION
[0005] The present application thus describes a power plant
configured to include a recirculation loop about which a working
fluid is recirculated. The recirculation loop may include a
plurality of components configured to accept an outflow of working
fluid from a neighboring upstream component and provide an inflow
of working fluid to a neighboring downstream component. The
recirculation loop may include: a recirculation compressor; an
upstream combustor positioned downstream of the recirculation
compressor; a high-pressure turbine positioned downstream of the
upstream combustor; a downstream combustor positioned downstream of
the high-pressure turbine; a low-pressure turbine positioned
downstream of the downstream combustor; and a recirculation conduit
configured to direct the outflow of working fluid from the
low-pressure turbine to the recirculation compressor. The power
plant further may include: an oxidant compressor configured to
provide compressed oxidant to one of the upstream combustor and the
downstream combustor; and means for extracting a portion of the
working fluid from an extraction point disposed at a predetermined
location on the recirculation loop.
[0006] These and other features of the present application will
become apparent upon review of the following detailed description
of the preferred embodiments when taken in conjunction with the
drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic drawing illustrating an exemplary
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0008] FIG. 2 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0009] FIG. 3 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0010] FIG. 4 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0011] FIG. 5 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0012] FIG. 6 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0013] FIG. 7 is a flow diagram illustrating an exemplary method of
operation relating to a power plant employing exhaust gas
recirculation and a reheat combustion system;
[0014] FIG. 8 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0015] FIG. 9 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a reheat combustion system;
[0016] FIG. 10 is a schematic drawing illustrating a configuration
of an alternative power plant employing exhaust gas recirculation
and a single combustion system;
[0017] FIG. 11 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a single combustion system;
[0018] FIG. 12 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a single combustion system; and
[0019] FIG. 13 is a schematic drawing illustrating an alternative
configuration of a power plant employing exhaust gas recirculation
and a single combustion system.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring now to the figures, where the various numbers
represent like parts throughout the several views, FIGS. 1 through
13 provided schematic illustrations of exemplary power plants
according to configurations of the present application. As will be
explained in further detail below, these power plants include novel
system architectures and configurations and/or methods of control
that achieve performance advantages given the recirculation of
exhaust gases. Unless otherwise stated, the term "power plant", as
used herein, is not intended to be exclusionary and may refer to
any of the configurations described herein, illustrated in the
figures, or claimed. Such systems may include two separate
turbines, exhaust gas recirculation, two combustion systems, and/or
a heat-recovery steam generator.
[0021] As illustrated in FIG. 1, the power plant 9 includes a
recirculation loop 10 that includes a recirculating flow of working
fluid. In certain embodiments of the present invention, as
illustrated in FIG. 1, the recirculation loop 10 is the means by
which exhaust gas from the turbines recirculates, thereby creating
a recirculating flow of working fluid. It will be appreciated that
recirculation loop 10 is configured such that each of the
components positioned thereon are configured to accept an outflow
of working fluid from a neighboring upstream component and provide
an inflow of working fluid to a neighboring downstream component.
Note that the several components of the recirculation loop 10 will
be described in reference to a designated "start position 8" on the
loop 10. It will be appreciated that the start position 8 is
arbitrary and the function of the system could be described in
another manner or in reference to another start position without
substantive effect. As shown, the start position 8 is positioned at
the intake of an axial compressor 12. As configured, the axial
compressor 12 accepts a flow of recirculated exhaust gases from the
turbines; accordingly, the axial compressor 12 is referred to
herein as "recirculation compressor 12". Moving in a downstream
direction, the recirculation loop 10 includes an upstream combustor
22, which is associated with a high-pressure turbine 30, and a
downstream combustor 24, which is associated with a low-pressure
turbine 32. It will be appreciated that the terms used to describe
these components are purposely descriptive so that efficient
description of the power plant 9 is possible. While the terms are
not meant to be overly limiting, it will be appreciated that the
"upstream" and "downstream" designations generally refer to the
direction of flow of working fluid through the recirculation loop
10 given the designated start position 8. Further, the
"high-pressure" and "low-pressure" designations are meant to refer
to the operating pressure levels in each turbine 30, 32 relative to
the other given the position of each turbine on the recirculation
loop 10.
[0022] Downstream of the low-pressure turbine 32, recirculation
conduit 40 channels exhaust gases to the intake of the
recirculation compressor 12, which thereby recirculates the exhaust
gases from the turbines (or, at least, a portion thereof). Several
other components may be positioned on the recirculation conduit 40.
It will be appreciated that these components may function to
deliver the exhaust gases to the recirculation compressor 12 in a
desired manner (i.e., at a desired temperature, pressure, humidity,
etc.). As shown, in various embodiments, a heat recovery steam
generator 39, a cooler 44, and a blower 46 may be included on the
recirculation conduit 40. In addition, the recirculation loop 10
may include a recirculation vent 41 which provides a way to
controllably vent an amount of exhaust from the recirculation
conduit 40 such that a desirable flow balance is achieved. For
example, it will be appreciated that under steady state conditions
an amount of exhaust must be vented through the recirculation vent
41 that approximately equals the amount of compressed oxidant and
fuel entering the recirculation loop 10 via the oxidant compressor
11 and fuel supply 20, respectively. It will be appreciated that
achieving a desired balance between oxidant/fuel injected into and
exhaust vented from the recirculation loop 10 may be done via
sensors recording the amount of compressed oxidant and fuel
entering the loop 10 and the amount of exhaust exiting, as well as,
temperature sensors, valve sensors, pressure sensors within the
recirculation loop 10, and other conventional means and
systems.
[0023] The power plant 9 may include an oxidant compressor 11,
which, unlike the recirculation compressor 12, is not fully
integrated into the recirculation loop 10. As provided below, the
oxidant compressor 11 may be an axial compressor that is configured
to inject compressed air or other oxidant at one or more locations
within the recirculation loop 10. In most applications, the oxidant
compressor 11 will be configured to compress air. It will be
appreciated that, in other embodiments, the oxidant compressor 11
may be configured to supply any type of oxidant which could be
pressurized and injected into the combustion system. For example,
the oxidant compressor 11 could compress a supply of air doped with
oxygen. The recirculation compressor 12, on the other hand, is
configured to compress recirculated exhaust gases from the turbines
30, 32. When necessary, a booster compressor 16 may be provided to
boost the pressure of the discharge of the oxidant compressor 11
before it is injected into the recirculation loop 10 so that a
preferable injection pressure is achieved. In this manner, the
compressed oxidant may be effectively delivered to one or more
combustors.
[0024] The oxidant compressor 11 and the recirculation compressor
12 may be mechanically coupled by a single or common shaft 14 that
drives both. A generator 18 may also be included on the common
shaft 14, while the high-pressure turbine 30 and the low-pressure
turbine 32 drive the common shaft 14 and the loads attached
thereto. It will be appreciated that the present invention may be
employed in systems having shaft configurations different than the
exemplary common shaft configuration 14 illustrated in the figures.
For example, multiple shafts may be used, each of which may include
one of the turbines and one or more of the load elements (i.e., one
of the compressors 11, 12 or the generator 18). Such a
configuration may include concentric shafts or otherwise.
[0025] In exemplary embodiments, the combustion system of the power
plant 9, as shown, includes an upstream combustor 22 and,
downstream of that, a downstream combustor 24. It will be
appreciated that, as discussed in more detail below, the upstream
combustor 22 and the downstream combustor 24 may include any type
of conventional combustors, combustion systems and/or reheat
combustors, and the chosen terminology refers only to relative
positioning on the recirculation loop 10 (given the designated
start position 8 and direction of flow). Typically, as depicted in
FIG. 1 and discussed in more detail below, the upstream combustor
22 operates by injecting into the recirculation loop 10 combustion
gas resulting from a fuel being combusted in a can combustor or
other type of conventional combustor. Alternatively, certain
combustion systems operate by direct fuel injection. Upon
injection, the injected fuel combusts within the recirculation loop
10. Either of these methods generally increases the temperature and
the kinetic energy of the working fluid, and either of the
combustor types may be employed as the upstream combustor 22 or the
downstream combustor 24. A fuel supply 20 may supply fuel, such as
natural gas, to the upstream combustor 22 and the downstream
combustor 24.
[0026] More specifically, the upstream combustor 22 may be
configured to accept the flow of compressed oxidant from the
oxidant compressor 11 and a fuel from the fuel supply 20. In this
mode of operation, the upstream combustor 22 may include one or
more cans or combustion chambers within which fuel and oxidant are
brought together, mixed, and ignited such that a high energy flow
of pressurized combustion gases is created. The upstream combustor
22 then may direct the combustion gases into the high-pressure
turbine 30, where the gases are expanded and work extracted. The
downstream combustor 24 may be configured to add energy/heat to the
working fluid at a point downstream of the high-pressure turbine
30. As shown in the embodiment of FIG. 1, the downstream combustor
24 may be positioned just upstream of the low-pressure turbine 32.
As stated, the downstream combustor 24 is so-called because it adds
heat/energy to the flow of working fluid at a point downstream of
the upstream combustor 22.
[0027] As one of ordinary skill in the art will appreciate, certain
operational advantages may be achieved using a dual combustion or
reheat system such as those described above. These advantages
include, among other things: 1) fuel flexibility; 2) improved
emissions; 3) lower overall firing temperatures; 4) less cooling
and sealing requirements; 5) longer part life; and 6) use of less
expensive materials due to lower firing temps. Accordingly,
improving the operation of power plants that include reheat
systems, as provided by the present invention, widens the potential
usage of reheat systems and the realization of the advantages these
systems typically provide.
[0028] As mentioned, the power plant 9 further includes
recirculation conduit 40. The recirculation conduit 40, in general,
forms the flow path by which exhaust from the turbines is
recirculated, thereby completing the recirculation loop 10. More
specifically, the recirculation conduit 40 directs the exhaust from
the low pressure turbine 32 on a path that ends at the intake of
the recirculation compressor 12. It will be appreciated that the
recirculation conduit 40 may circulate the exhaust through several
components along the way, including, as indicated in FIG. 1, a
heat-recovery steam generator 39, a cooler 44, and a blower 46.
(Note that, to avoid unnecessary complexity, the heat-recovery
steam generator 39 has been represented in a simplified form in
FIG. 1.) Those of ordinary skill in the art will appreciate that
the heat-recovery steam generator 39 of the present invention may
include any type of system in which combustion exhaust from one or
more combustion turbines is used as the heat source for the boiler
of a steam turbine.
[0029] Downstream of the heat-recovery steam generator 39, the
cooler 44 may be positioned such that gases flowing through the
recirculation conduit 40 flow through it. The cooler 44 may include
a direct contact cooler or other conventional heat exchanger that
suffices for this function, and may operate by extracting further
heat from the exhaust gases such that the exhaust gases enter the
recirculation compressor 12 at a desired or preferred temperature.
The cooler 44 may also provide means by which humidity levels
within the recirculated gases is controlled to preferable levels.
That is, the cooler 44 may extract water from the flow through
cooling it, which thereby lowers the humidity level of the
recirculated gases upon the gases being heated to the temperature
of the flow before entering the cooler. As illustrated in FIG. 1,
the blower 46 may be located downstream of the cooler 44; however,
as one of ordinary skill in the art will appreciate, this order may
be reversed. The blower 46 may be of a conventional design. The
blower 46 may function to more efficiently circulate the exhaust
gases through the recirculation conduit 40 such that the gases are
delivered to the intake of the recirculation compressor 12 in a
desired manner.
[0030] The power plant 9 may include several types of conduits,
pipes, valves, sensors and other systems by which the operation of
the power plant 9 is controlled and maintained. It will be
appreciated that all valves described herein may be controlled to
various settings that affect the amount of fluid passing through
the conduit. As already described, the recirculation conduit 40
recirculates exhaust gases from the turbines 30, 32 to the intake
of the recirculation compressor 12, thereby providing a
recirculating flow path for the working fluid. In addition, as
indicated in FIG. 1, a first oxidant conduit 52 may be provided
that directs the compressed oxidant from the oxidant compressor 11
to the upstream combustor 22. The first oxidant conduit 52 may
include an oxidant valve 54 that controls the flow of oxidant
through this conduit. The first oxidant conduit 52 further may
include the booster compressor 16, which, as described in more
detail below, may be used to boost the pressure of the compressed
oxidant within this conduit. The first oxidant conduit 52 may
further include a vent valve 56. The vent valve 56 provides means
by which a portion of the compressed oxidant moving through the
first oxidant conduit 52 is vented to atmosphere. As indicated in
FIG. 1, certain embodiments of the present invention operate by
providing a flow of compressed oxidant from the oxidant compressor
11 to the upstream combustor 22, but not the downstream combustor
24. In other embodiments, such as those shown in FIGS. 2 through 5,
the present invention operates by providing a flow of compressed
oxidant from the oxidant compressor 11 to the upstream combustor 22
and the downstream combustor 24. In still other embodiments, the
present invention operates by providing a flow of compressed
oxidant from the oxidant compressor 11 to the downstream combustor
22 but not the upstream combustor 24. This type of system, for
example, is represented in FIGS. 2 and 4 when the oxidant valve 54
on the first oxidant conduit 52 is completely shut (i.e., set so
that no flow from the oxidant compressor 11 is allowed to pass
therethrough).
[0031] The fuel supply 20 may include two supply conduits that
provide fuel to the upstream combustor 22 and/or the downstream
combustor 24. As shown, a fuel valve 58 controls the amount of fuel
being delivered to the upstream combustor 22, while another fuel
valve 59 controls the amount of fuel being delivered to the
downstream combustor 24. It will be appreciated that, though not
shown in the figures, the fuel types delivered to the upstream
combustor 22 and the downstream combustor 24 do not have to be the
same, and that the use of different fuel types may be advantageous
given certain system criteria. In addition, as discussed in more
detail below, the fuel valve 58 and the fuel valve 59 may be
controlled so that fuel is delivered to only one of the two
combustors 22, 24. More specifically, in certain embodiments, the
fuel valve 58 may be completely shut so that fuel is not delivered
to the upstream combustor 22. In this case, as discussed in more
detail below, both combustors 22, 24 may operate per the fuel
delivered to the downstream combustor 24. Similarly, in certain
embodiments, the fuel valve 59 may be completely shut so that fuel
is not delivered to the downstream combustor 22. In this case, as
discussed in more detail below, both combustors 22, 24 may operate
per the fuel delivered to the upstream combustor 22. It will be
appreciated that systems described herein as operating with a valve
that is shut completely is intended to cover system configurations
where the conduit on which the shut valve is positioned is omitted
altogether.
[0032] An extraction point 51 comprises the point at which gases
are extracted from the working fluid. In preferred embodiments, the
extraction point 51 is positioned on the recirculation loop 10 such
that carbon dioxide (CO.sub.2) and/or nitrogen (N.sub.2) may be
efficiently extracted. Given certain modes of operation and system
control, the system architecture of the present invention allows
for such extraction to occur at a position that, as illustrated in
FIG. 1, is upstream of both the high-pressure turbine 30 and the
upstream combustor 22. More specifically, as shown, the extraction
point 51 may be located at a position that is just upstream of the
combustion reaction in the upstream combustor 22. The extraction
point 51 may include conventional extracting means by which a
portion of the gases within the working fluid are diverted into a
conduit and, thereby, removed from the recirculation loop 10. An
extracted gas valve 61 may be provided to control the amount of
working fluid that is extracted. Downstream of the extracted gas
valve 61, the conduit may deliver an extracted gas supply 62 to one
or more downstream components (not shown). In preferred
embodiments, the extracted gas supply 62 may be directed to a
separation system (not shown) that separates the carbon dioxide
from the nitrogen per conventional means. As stated, after
separation, these gases may be used in many types of industrial
applications, such as, for example, applications in the food and
beverage industry.
[0033] Branching from the conduit that connects to the extraction
point 51, a turbine bypass conduit 63 also may be included that
provides a pathway that bypasses each of the turbines 30, 32. The
turbine bypass conduit 63 is provided for startup situations, and,
because it does not meaningfully impact the function of the present
invention, will not be discussed further.
[0034] In other embodiments, the extraction point 51 may be located
in different locations within the recirculation loop 10 of FIG. 1.
As described in more detail below (particularly with regard to
FIGS. 5 and 6), the architecture and control methods provided
herein teach efficient and effective means by which one of the
combustors 22, 24 may be operated at or near the stoichiometric
point or a preferred stoichiometric ratio. That is, the fuel and
oxidant supply within the power plant 9 may be controlled in such a
way that, once the oxidant and fuel have adequately mixed, ignited
and combusted within one of the combustors 22, 24, an exhaust that
is free or substantially free of oxygen and unspent fuel is
produced. In this condition, the exhaust consists of high levels of
carbon dioxide and nitrogen, which may be economically extracted
for use in other applications. As stated, "operation at the
stoichiometric point" or "stoichiometric point operation" refers to
operation at, near or within an acceptable or desired range about
the stoichiometric point. It will be appreciated that
"stoichiometric point" may also be referred to a stoichiometric
ratio of 1, as it is said to include a 1-to-1 ratio of fuel and
oxidant. It will further be appreciated that ratios that are
greater than 1 are described as containing excess oxidant, while
ratios less than 1 are described as containing excess fuel. It will
be appreciated that, depending on the limitations of a particular
power plant, the desired properties of the extracted working fluid,
as well as other criteria, stoichiometric point operation may refer
to stoichiometric operation within a range about the stoichiometric
point or, put another way, a stoichiometric ratio of 1.
Accordingly, in certain embodiments, "stoichiometric point
operation" may refer to operation within the range of
stoichiometric ratios defined between 0.75 and to 1.25. In more
preferable embodiments, "stoichiometric point operation" may refer
to operation within the range of stoichiometric ratios defined
between 0.9 and to 1.1. In still more preferable embodiments,
"stoichiometric point operation" may refer to operation that is
substantially at or very close to a stoichiometric ratio of 1.
Finally, in other preferable embodiments, "stoichiometric point
operation" may refer to operation within the range of
stoichiometric ratios defined between approximately 1.0 and to
1.1.
[0035] It will be appreciated that if one of the combustors 22, 24
is operated at the stoichiometric point (i.e., a stoichiometric
ratio of 1 or within one of the predefined ranges described above
or another desired range), the exhaust downstream of the combustor
is substantially devoid of unspent fuel and oxygen, and consists
substantially of carbon dioxide and nitrogen gas (and/or some other
desirable gaseous characteristic), which may be economically
extracted. As a result of this, pursuant to embodiments of the
present invention, the extraction point 51 generally may be located
at any point on the recirculation loop 10 that is both: 1)
downstream of the whichever combustor 22, 24 is operating at the
stoichiometric point and 2) upstream of the other combustor 22, 24.
(It will be appreciated by those of ordinary skill in the art that
"upstream of the other combustor", as used herein, means upstream
of the point within the combustor at which oxidant and/or fuel
actually enters the recirculation loop 51, and that, because of
this, "upstream of the other combustor" may include areas that
might be construed as within the "other combustor" but which are
also upstream of the position at which oxidant and/or fuel is
injected into the flow of working fluid, such as, for example,
certain areas within a combustor head-end. In a configuration like
FIG. 1, assuming that the fuel input of the downstream combustor 24
is controlled to produce combustion at (or substantially at) the
stoichiometric point, the extraction point 51 may be located at any
point within a range defined between the downstream combustor 24
and, proceeding in a downstream direction, the upstream combustor
22. In one preferred embodiment, as illustrated in FIG. 1, the
extraction point may be located within this range at the discharge
of the recirculation compressor 12. It will be appreciated that
this location provides extracted gas that is highly pressurized,
which may be advantageous in certain downstream uses.
[0036] The power plant 9 may further include one or more sensors 70
that measure operating parameters, settings, and conditions within
the components and various conduits of the system. One such sensor
may be a sensor for detecting excess oxidant 64, such as, for
example, a conventional oxygen sensor. The sensor for detecting
excess oxidant 64 may be positioned just upstream of the extraction
point 51 and may measure at predefined intervals the oxygen content
of the exhaust or working fluid flowing through the recirculation
loop 10. Positioned thusly, the sensor for detecting excess oxidant
64 may be well situated to test the working fluid for oxidant
content, which may provide information as to stoichiometric ratio
within the combustor directly upstream of the sensor for detecting
excess oxidant 64 and/or whether extraction of the working fluid
would yield a gas supply that is suitably free of oxidant and
unspent fuel. It will be appreciated that the sensor for detecting
excess oxidant 64 may be positioned within a range on the
recirculation loop 10 that is defined between the extraction point
51 and, proceeding in the upstream direction, the first combustor
22, 24 that is encountered. It will be appreciated that, given the
positioning of the extraction point 51, the first combustor 22, 24
encountered in the upstream direction is the combustor 22, 24 which
is being controlled at the preferred stoichiometric ratio. In this
manner, the sensor for detecting excess oxidant 64 may be used to
determine the current desirability of extracting gas from the
recirculation loop 10. As described in more detail below, the
system may include other sensors 70 that measure a host of process
variables that may relate to any of the components of the system.
Accordingly, the figures indicate a plurality of sensors 70 at
exemplary locations about the power plant 9. As one of ordinary
skill in the art will appreciate, conventional systems typically
include many sensors other than just those represented in the
several figures, and, further, that those other sensors may be
located in other locations within the system than just those
indicated. It will be appreciated that these sensors 70 may
electronically communicate their readings with the control unit 65
and/or function pursuant to instructions communicated to them by
the control unit 65. One such sensor 70 that could be used either
together or interchangeably with the sensor for detecting excess
oxidant 64 is a sensor that detects the presence of unspent fuel in
the exhaust. Teamed with the sensor for detecting excess oxidant
64, a sensor for detecting unspent fuel 70 could provide
measurements from which the stoichiometric ratio in the upstream
combustor 22, 24 could be determined as well as the current
suitability of extracting working fluid. Those skilled in the art
will appreciate that other sensors may be used to collect data
concerning the stoichiometric properties of the combustion
occurring within the combustors. For example, a CO sensor and a
humidity sensor may be used.
[0037] The power plant 9 may further include a control unit 65 that
functions according to certain embodiments described herein. It
will be appreciated that the control unit 65 may include an
electronic or computer implemented device that takes in data from
sensors and other sources regarding plant operational parameters,
settings, and conditions, and, pursuant to algorithms, stored data,
operator preferences, etc., controls the settings of the various
mechanical and electrical systems of the power plant 9 such that
desired modes of operation are achieved. For example, the control
unit 65 may control the power plant 9 such that stoichiometric
operation or operation at a preferred stoichiometric ratio is
achieved in one of the combustors 22, 24. It will be appreciated
that the control mechanism may achieve this objective by balancing
the fuel and oxidant injected into the either the upstream or
downstream combustor 22, 24, as well as taking into account any
excess oxidant or unspent fuel from the other of the two combustor
22, 24 that travels within the recirculating working fluid. Once
stoichiometric operation is achieved, the control unit 65 may
control the extracted gas valve 61 such that extraction takes place
at a desired rate and for a desired period of time or until
changing conditions make the extraction no longer suitable. The
settings of the various valves described above that govern the flow
of working fluid, extraction of gases, fuel consumption, etc. may
be controlled pursuant to electrical signals, which may be sent via
wired or wireless communication connections, received from the
control unit 65.
[0038] In use, the power plant 9 according to an exemplary
embodiment may operate as follows. The rotation of blades within
oxidant compressor 11 compresses oxidant that is supplied, via the
first oxidant conduit 52 to the upstream combustor 22. Before
reaching the upstream combustor 22, the booster compressor 16 may
be provided in some embodiments. The booster compressor 16 may be
used to increase the pressure of the oxidant being supplied by the
oxidant compressor 11 to a level that is adequate or preferable for
injection into the upstream combustor 22. In this manner, the flow
of compressed oxidant may be joined within the upstream combustor
22 with a flow of compressed exhaust gases, which is supplied to
the combustor from the recirculation compressor 12. It will be
appreciated that successfully bringing together two such flows
within the upstream combustor 22 may be accomplished in several
ways and that, depending on how the flows are introduced within the
upstream combustor 22, suitable pressure levels for each may vary.
The present invention teaches methods and system configurations by
which pressure levels may be controlled such that the flows may be
combined in a suitable manner, while avoiding avoidable aerodynamic
losses, backflow, and other potential performance issues.
[0039] Accordingly, the upstream combustor 22 may be configured to
combine the flow of compressed oxidant from the oxidant compressor
11 with the flow of compressed exhaust gases from the recirculation
compressor 12 and combust a fuel therein, producing a flow of
high-energy, pressurized combustion gases. The flow of combustion
gases then is directed over the stages of rotating blade within the
high-pressure turbine 30, which induces rotation about the shaft
14. In this manner, the energy of the combustion gases is
transformed into the mechanical energy of the rotating shaft 14. As
described, the shaft 14 may couple the high-pressure turbine 30 to
the oxidant compressor 11 so that the rotation of the shaft 14
drives the oxidant compressor 11. The shaft 14 further may couple
the high-pressure turbine 30 to the recirculation compressor 12 so
that the rotation of the shaft 14 drives the recirculation
compressor 12. The shaft 14 also may couple the high-pressure
turbine 30 to the generator 18 so that it drives the generator 18
as well. It will be appreciated that the generator 18 converts the
mechanical energy of the rotating shaft into electrical energy. Of
course, other types of loads may be driven by the high-pressure
turbine 30.
[0040] The working fluid (i.e., the exhaust from the high-pressure
turbine 30) then is directed to the low-pressure turbine 32. Before
reaching the low-pressure turbine 32, the downstream combustor 24
adds heat/energy to the working fluid flowing through the
recirculation loop 10, as described above. In the embodiment of
FIG. 1, the downstream combustor 24 is configured to combust a fuel
within the exhaust from the high-pressure turbine 30. In
alternative embodiments, as shown in FIGS. 2-6 and discussed in
more detail below, the downstream combustor 24 may be configured to
combine a flow of compressed oxidant from the oxidant compressor
with the flow of exhaust gases from the high-pressure turbine 30
and combust a fuel therein, producing a flow of high-energy,
pressurized combustion gases. The working fluid then is directed
over the stages of rotating blades within the low-pressure turbine
32, which induces rotation about the shaft 14, thereby transforming
the energy of the combustion gases into the mechanical energy of
the rotating shaft 14. As with the high-pressure turbine 30, the
shaft 14 may couple the low-pressure turbine 32 to the oxidant
compressor 11, the recirculation compressor 12, and/or the
generator 18. In certain embodiments, the high-pressure turbine 30
and the low-pressure turbine 32 may drive these loads in tandem. In
other embodiments, concentric shafts may be used such that the
high-pressure turbine 30 drives part of the load on one of the
concentric shafts, while the low-pressure turbine 32 drives the
remaining load on the other. Additionally, in other system
configurations, the high-pressure turbine 30 and the low-pressure
turbine 32 may drive separate, non-concentric shafts (not
shown).
[0041] From the low-pressure turbine 32, recirculation conduit 40
may form a flow path that completes the recirculation loop 10 of
the present invention. This flow path, ultimately, delivers the
exhaust gases from the turbines 30, 32 to the intake of the
recirculation compressor 12. As part of this recirculation conduit
40, the exhaust gases may be used by the heat-recovery steam
generator 39. That is, the exhaust gases may provide a heat source
for the boiler that drives a steam turbine which receives steam
from the heat-recovery steam generator 39. Downstream of that, the
exhaust gases may be further cooled by the cooler 44 as well as
being passed through a blower 46. The cooler 44 may be used to
lower the temperature of the exhaust gases so that they are
delivered to the intake of the recirculation compressor 12 within a
desired temperature range. The blower 46 may assist in circulating
the exhaust gases through the recirculation loop 10. It will be
appreciated that the heat recovery steam generator 39, the cooler
44 and the blower 46 may include conventional components and be
operated pursuant to conventional methods.
[0042] In regard to the operation of the control unit 65, it will
be appreciated that it may include an electronic or computer
implemented device that takes in data regarding plant operational
parameters and conditions, and, pursuant to algorithms, stored
data, operator preferences, etc., controls the settings of the
various mechanical and electrical systems of the power plant 9 such
that desired modes of operation are achieved--for example,
achieving operation at or substantially at the stoichiometric
point. The control unit 65 may include control logic specifying how
the mechanical and electrical systems of the power plant 9 should
operate. More specifically, and in accordance with certain
embodiments of the present application, the control unit 65
typically includes programmed logic that specifies how certain
operating parameters/stored data/operator preferences/etc. should
be monitored and, given certain inputs from the monitored data, how
the various mechanical and electrical systems of the power plant 9,
such as those described above, should be operated. The control unit
65 may control the operation of the various systems and devices
automatically in response to the dictates of the control logic, or,
in certain instances, may seek operator input before actions are
taken. As one of ordinary skill in the art will appreciate, such a
system may include multiple sensors, devices, and instruments, some
of which are discussed above, that monitor relevant operational
parameters. These hardware devices may transmit data and
information to the control unit 65, as well as being controlled and
manipulated by the control unit 65. That is, pursuant to
conventional means and methods, the control unit 65 may receive
and/or acquire data from the systems of the power plant 9, process
the data, consult stored data, communicate with the operators of
the power plant 9, and/or control the various mechanical and
electrical devices of the system pursuant to a set of instructions
or logic flow diagrams, which, as one of ordinary skill in the art
will appreciate, may be made part of a software program that is
operated by control unit 65, and which may include aspects relating
to embodiments of the present invention. In short, the control unit
65 may control operation of the power plant 9 such that it operates
at the stoichiometric point and, while operating thusly, extracts a
supply of combustion exhaust that is substantially devoid of oxygen
and unspent fuel. Discussion below, in relation to FIG. 7, relates
to logic flow diagrams according to the present invention for
operating the systems described herein at the stoichiometric point
and extraction of desirable exhaust gas. It will be appreciated
that these logic flow diagrams may be used by the control unit for
such purposes.
[0043] FIGS. 2 through 6 provide embodiments of the present
invention that include alternative system configurations. It will
be appreciated that these configurations present alternative
strategies for injecting oxidant from the oxidant compressor 11
into the recirculation loop 10, delivering fuel to the combustion
systems, and the manner in which exhaust gases may be extracted.
Each of these alternatives offers certain advantages, including the
manner in which stoichiometric operation may be achieved and
maintained. It will be appreciated that these alternatives are
exemplary and not intended to provide an exhaustive description of
all possible system configurations which might fall within the
scope of the appended claims. In addition, while FIGS. 2 through 6
illustrate both fuel and oxidant being delivered to each of the
upstream and the downstream combustor 22, 24, it will be
appreciated that certain embodiments described below function in
systems in which oxidant is delivered to only one of the upstream
and downstream combustors 22, 24 and/or systems in which fuel is
delivered to only one of the upstream and downstream combustors 22,
24. Examples of any of these systems may be constructed via control
of the various valves 54, 58, 59, 68 that deliver oxidant and fuel
to the combustors 22, 24.
[0044] FIG. 2 through 4 provide embodiments that include a second
oxidant conduit 67 and oxidant valve 68, which together may be used
to supply a controlled compressed oxidant amount (which like the
first oxidant conduit 52 is derived from the oxidant compressor 11)
to the downstream combustor 24. As shown in FIGS. 2 and 3, the
second oxidant conduit 67 may branch from the first oxidant conduit
52, which means that the compressed oxidant for each is drawn from
the same supply point from the oxidant compressor 11. In FIG. 2,
the branching occurs such that a connection with the first oxidant
conduit 52 occurs upstream of the oxidant valve 54 and booster
compressor 16 of the first oxidant conduit 52. In this case, the
second oxidant conduit 67 thereby bypasses the booster compressor
16. This may be useful in creating flows of differing pressures
levels within the first oxidant conduit 52, which would have a
higher pressure due to the booster compressor 16 than that within
the second oxidant conduit 67. As the first oxidant conduit 52
provides compressed oxidant to a point on the recirculation loop 10
upstream of the second oxidant conduit 67, this configuration
allows for an efficient means by which the pressure in each may be
controlled to a pressure level that is appropriate for injection at
the different locations. In FIG. 3, the branching occurs downstream
of the oxidant valve 54 of the first oxidant conduit 52. More
specifically, the branching of the second oxidant conduit 52 occurs
between the oxidant valve 54 of the first oxidant conduit 52 (which
may be positioned downstream of the booster compressor 16, as
shown) and combustor 22.
[0045] As illustrated in FIG. 4, the second oxidant conduit 67 may
also be independent of the first oxidant conduit 52. As shown, in
this instance, the second oxidant conduit 67 may extend from an
extraction point within the oxidant compressor 11. The extraction
point for the second oxidant conduit may be located at one of the
stages that is upstream of the position where the first oxidant
conduit 52 derives its flow of compressed oxidant, which, for
example, may be located in the compressor discharge casing. More
specifically, the extraction point may be configured to bleed
compressed oxidant at an intermediate stage within the oxidant
compressor 11. With the first oxidant conduit 52 drawing from the
compressor discharge casing or in proximity thereto, this
arrangement results in a higher pressure flow of compressed oxidant
through the first oxidant conduit 52 than that in the second
oxidant conduit 67. It again will be appreciated that this
configuration allows the first and second oxidant conduits 52, 67
to have differing pressure levels without the need of including a
booster compressor 16. As before, the pressure differential may be
useful in that the pressure of the compressed oxidant may be
matched to the pressure at the position on the recirculation loop
10 it is used.
[0046] FIGS. 5 and 6 provide differing strategies for locating the
extraction point 51 given the fact that both combustors 22, 24
receive a supply of compressed oxidant from the oxidant compressor
11. It will be appreciated that configuring the system to have two
points at which oxidant/fuel are combusted provides new
alternatives for producing operation at the stoichiometric point
(note that, as stated, this refers to operation within a desired
range about or near the stoichiometric point), and, thus, differing
locations (as provided in FIGS. 5 and 6) at which working fluid may
be extracted. As described, the architecture and control methods
provided herein teach efficient and effective means by which power
plants may be operated at the stoichiometric point. The fuel and
oxidant supply to the power plant 9 may be controlled in such way
that, once the oxygen (from the injected oxidant) and fuel have
adequately mixed, ignited and combusted, an exhaust that is
substantially free of oxygen and unspent fuel is produced. As a
result of this, pursuant to embodiments of the present invention,
the extraction point 51 may be located at any point on the
recirculation loop 10 that has exhaust derived from stoichiometric
point operation. As described above in relation to the
configuration of FIG. 1, this generally means that the extraction
point may be located at any position on the recirculation loop 10
that is both: 1) downstream of the combustor 22, 24 which is being
operated at the stoichiometric point; and 2) upstream of the other
combustor 22, 24. It will be appreciated that more than one
extraction point within this range may be provided, and that this
arrangement may be useful where different pressure levels are
useful for a plurality of extracted gas supplies.
[0047] FIG. 5 illustrates an exemplary configuration having an
extraction point 51 that is positioned near the aft end of the
high-pressure turbine 30. It will be appreciated that this
extraction point 51 may prove effective when the upstream combustor
22 operates at the stoichiometric point. Given the principles
discussed above and assuming this operation, possible extraction
points 51 constitute a range defined between the upstream combustor
22 and, proceeding in the downstream direction, the downstream
combustor 24. That is, pursuant to embodiments of the present
invention, the power plant 9 may be controlled such that the
combined effect of the oxidant and fuel introduced within the
combustors 22, 24 produces combustion within the upstream combustor
22 at a preferred stoichiometric ratio, which thereby creates a
range of positions downstream of the upstream combustor 22 in which
extraction of working fluid having desired characteristics may be
achieved.
[0048] FIG. 6 illustrates an exemplary configuration having an
extraction point 51 that is positioned just upstream of the heat
recovery steam generator 39. It will be appreciated that this
extraction point 51 may prove effective when the downstream
combustor 24 operates at the stoichiometric point. Given the
principles discussed above and assuming this operation, possible
extraction points 51 constitute a range defined between the
downstream combustor 24 and, proceeding in the downstream
direction, the upstream combustor 22. That is, pursuant to
embodiments of the present invention, the power plant 9 may be
controlled such that the combined effect of the oxidant and fuel
introduced within the combustors 22, 24 produces combustion within
the downstream combustor 24 at a preferred stoichiometric ratio,
which thereby creates a range of positions downstream of the
downstream combustor 24 in which extraction of the working fluid
having desired characteristics may be achieved.
[0049] FIG. 7 illustrates a logic flow diagram 100 for a method of
operating the power plant 9 according to an exemplary embodiment of
the present invention. As one of ordinary skill in the art will
appreciate, the logic flow diagram 100 is exemplary and includes
steps which may not be included in the appended claims. Further,
any function described above in relationship to the several
components of the system is incorporated into the discussion below
where necessary or possible to aid in the carrying out of the
specified steps. The logic flow diagram 100 may be implemented and
performed by the control unit 65. In some embodiments, the control
unit 65 may comprise any appropriate high-powered solid-state
switching device. The control unit 65 may be a computer; however,
this is merely exemplary of an appropriate high-powered control
system, which is within the scope of the present application. In
certain embodiments, the control unit 65 may be implemented as a
single special purpose integrated circuit, such as ASIC, having a
main or central processor section for overall, system-level
control, and separate sections dedicated to performing various
different specific combinations, functions and other processes
under control of the central processor section. It will be
appreciated by those skilled in the art that the control unit also
may be implemented using a variety of separate dedicated or
programmable integrated or other electronic circuits or devices,
such as hardwired electronic or logic circuits including discrete
element circuits or programmable logic devices. The control unit 65
also may be implemented using a suitably programmed general-purpose
computer, such as a microprocessor or microcontroller, or other
processor device, such as a CPU or MPU, either alone or in
conjunction with one or more peripheral data and signal processing
devices. In general, any device or similar devices on which a
finite state machine capable of implementing the logic flow diagram
100 may be used as the control unit 65.
[0050] It will be appreciated that, in one possible environment,
the control unit 65 may include a General Electric SPEEDTRONIC.TM.
Gas Turbine Control System, such as is described in Rowen, W. I.,
"SPEEDTRONIC.TM. Mark V Gas Turbine Control System", GE-3658D,
published by GE Industrial & Power Systems of Schenectady, N.Y.
The control unit 65 may be a computer system having a processor(s)
that executes programs to control the operation of the gas turbine
using sensor inputs and instructions from human operators. The
programs executed by the control unit 65 may include scheduling
algorithms for regulating the components of the power plant 9. The
commands generated by the control unit 65 may cause actuators
within any of the components to, for example, adjust valves between
the fuel supply and combustors 22, 24 that regulate the flow and
type of fuel, inlet guide vanes on the compressors 11, 12, and
other control settings on the turbine 30, 32. Further, the control
unit 65 may regulate the power plant 9 based, in part, on
algorithms stored in computer memory of the control unit 65. These
algorithms, for example, may enable the control unit 65 to maintain
emission levels in exhaust to within certain predefined limits, to
maintain the combustor firing temperature to within predefined
temperature limits, or another maintain operational parameter
within a predefined range.
[0051] Returning to FIG. 7, one of ordinary skill in the art will
appreciate that, in general, flow diagram 100 illustrates an
example of how a feedback loop may be structured to provide an
iterative process for controlling stoichiometry within one of the
combustors and/or extraction level of exhaust having desired
characteristics. It will be appreciated that the several steps of
such a process may be described in many different ways without
deviating from the central idea of the process set forth herein.
The control methods described herein may be implemented via a
feedback loop that is used in conjunction with control algorithms,
such as a PID control algorithm, though other control algorithms
also may be used.
[0052] Logic flow diagram 100 may begin at a step 102, which
includes monitoring and measuring the operating conditions and
process variables (which will be referred to generally as "process
variables") of the power plant 9. Process variables, as used
herein, represent the current status of the system or process that
is being controlled. In this case, process variables may include
any operating parameter that may be measured by any type of sensor.
More specifically, at step 102, the control unit 65, pursuant to
any of the methods discussed above or any conventional systems
(either current or developed in the future), may receive, monitor,
and record data relating to the operation of the power plant 9. The
operation of the power plant 9 and the several components related
thereto may be monitored by several sensors 70 detecting various
conditions of the system and environment. For example, one or more
of the following process variable may be monitored by the sensors
70: temperature sensors may monitor ambient temperature surrounding
the plant 9, inlet and discharge temperatures of the compressors
11, 12, exhaust temperature and other temperature measurements
along the hot-gas path of the turbines 30, 32, pressure sensors may
monitor ambient pressure, and static and dynamic pressure levels at
the inlet and outlet of the compressors 11, 12, and exhaust of the
turbines 30, 32, as well as at other locations in the gas stream.
Sensors 70 further may measure the extraction level at the
extraction point 51, fuel flow to each of the combustors 22, 24,
gas composition within the recirculated exhaust gas or working
fluid (which may include oxidant sensor 64 as well as other sensors
that measure levels of unspent fuel or CO or other gases within the
exhaust gas), temperature and pressure of the recirculated exhaust
gas along the recirculation conduit 10, including parameters
relating to the operation of the heat recovery steam generator 39,
the cooler 44, and the blower 46. The sensors 70 may also comprise
flow sensors, speed sensors, flame detector sensors, valve position
sensors, guide vane angle sensors, and the like that sense various
parameters pertinent to the operation of power plant 9, which may
include oxidant flow characteristics through the first oxidant
conduit 52 and the second oxidant conduit 67. It will be
appreciated that the system may further store and monitor certain
"specified set-points" that include operator preferences relating
to preferred or efficient modes of operation. It further will be
appreciated that the measuring, monitoring, storing and/or
recording of process variables and/or specified set-point may occur
continuously or at regular intervals, and that updated or current
data may be used throughout any of the several steps of logic flow
diagram 100 whether or not there is a direct line in FIG. 7
connecting step 102 to the other steps. From step 102, the process
may continue to step 104.
[0053] At a step 104, the method may determine whether whichever
combustor 22, 24 is configured to operate at a preferred
stoichiometric ratio (which may include a range of suitable
stoichiometric ratios) is, in fact, operating at the preferred
stoichiometric ratio. It will be appreciated that this may be
accomplished by comparing measured process variables, calculating
current conditions, and comparing current conditions to specified
set-points. If it is determined that this mode of operation is
occurring, the method may proceed to step 106. If it is determined
that this mode of operation is not occurring, the method may
proceed to step 114.
[0054] It will be appreciated that the determination as to whether
the relevant combustor 22, 24 is operating at the preferred
stoichiometric ratio may be achieved in several ways and that, once
determined, a feedback loop using one or more control inputs may be
used to control the system within this preferred mode or cause the
system to operate in this manner. One method may be to detect or
measure the content of the exhaust gases being emitted from the
relevant combustor. This may include sensors 70, such as the sensor
for detecting excess oxidant 64, that measures the gases present in
the exhaust and/or other relevant characteristics. It will be
appreciated that a sensor 70 that detects the presence of unspent
fuel or CO or other gases within the exhaust flow may be used also.
Measuring the flow characteristics of the inputs (i.e., the oxidant
and the fuel) to one of the combustors also may be used to
determine if combustion within the relevant combustor is occurring
at the preferred stoichiometric ratio. In this case, for example,
the oxidant flow into the combustor may be measured, the fuel flow
into the combustor may be measured, and a determination made as to
the stoichiometric characteristics of the combustion therein given
these inputs. Other relevant operating characteristics (such as
temperature, pressure, etc.) may also be taken into account.
Alternatively, or in conjunction with this calculation, unspent
fuel or CO or other gases and/or oxygen may be measured downstream
of the combustors or other points within the circulating flow of
working fluid. From this, a calculation may be made as to the
stoichiometric balance of the combustion, which may then be
compared with the specified set-point or preferred stoichiometric
ratio to determine if it falls within an acceptable range.
[0055] At step 106, having already determined that one of the
combustors is operating within the desired stoichiometric range,
the logic flow diagram 100 may determine the current level of
extraction at extraction point 51. This may be done via checking
measured process variables which either indicate this flow level
directly or may be used to calculate the amount of gas being
extracted. The method may further check whether the current level
of extraction satisfies a desired level of extraction or specified
set-point. This may be done by comparing the actual level of
extraction (which may be measured) to operator defined set-points
or preference. If it is determined that the desired level of
extraction is being satisfied, the method may cycle back to step
102 where the process begins anew. If it is determined that the
desired level of extraction is not being satisfied, the method may
proceed to step 108.
[0056] At step 108, the method determines one or more "control
inputs" that may be used to manipulate the function of system
components in such a way as to achieve the desired level of
extraction or, at least, to achieve an extraction level that
decreases the difference between the actual level of extraction and
the desired level of extraction. It will be appreciated that a
"control input" is one of the many ways by which operation of the
power plant 9 or any of its components may be controlled or
manipulated. These, for example, may include level of fuel flow to
the combustors 22, 24, control of oxidant flow to the combustors
22, 24, angle of inlet guide vanes within the compressors 11, 12,
etc. Whereas, a "variance amount" is the extent to which a control
input must be manipulated to bring about the desired manner of
operation. The variance amount, for example, may include the extent
to which the fuel flow to the combustors 11, 12 must be increased
or decreased to bring about desired operation. In certain
embodiments, one of the control inputs that is particularly
relevant at step 108 is the setting of the extracted gas valve 61.
In this case, the variance amount is the extent to which the
setting of the valve 61 needs to be manipulated so that a desired
extraction level is achieved. The method may then proceed to step
110. It will be appreciated that a conventional feedback control
mechanism in conjunction with a PID controller or the like may be
used to achieve control as specified herein. Thus, an iterative
process of variations to one or more control inputs may bring the
system toward desired operation.
[0057] At step 110, in some embodiments, the method may determine
the probable effects to plant operation of each of the available
control inputs/variance amounts from step 108 before making the
actual change to the control input. It will be appreciated that
these types of calculations may be achieved per conventional power
plant control programs and modeling software, such as those systems
and methods mention herein and others similar to them. It further
will be appreciated that these calculations may involve an
iterative process that takes into account efficient control
measures/counter-measures which may be made in response to the
proposed variance of the relevant control input, economic
considerations, wear and tear to the power plant, operator
preferences, plant operational boundaries, etc. The method then may
proceed to Step 112.
[0058] At step 112, the process 100 may determine which of the
available control inputs/variance amounts from the above step is
most favorable or preferred. This determination, in large part, may
be based upon the effects to system operation that were calculated
in step 110. Then, for whichever control input/variance amount is
deemed most favorable, the method may determine if the proposed
control input/variance amount should be executed based on whether
the associated benefits of meeting extraction demand outweighs the
costs associated with executing the variance amount. It will be
appreciated that economic considerations and operator preferences
may be included in this determination. Based on this calculation,
the method then may execute the proposed control input/variance
amount or not. The method then may return to step 102, and an
iterative process begun by which a preferred level of extraction is
achieved.
[0059] As described above, if at step 104 it is determined that the
relevant combustor is not operating at the stoichiometric point,
the method may proceed to step 114. At step 114, the method may
determine one or more control inputs/variance amounts that are
available for achieving stoichiometric point operation within the
relevant combustor. As before, control inputs include ways in which
operation of the power plant 9 may be altered, manipulated or
controlled, and the variance amount is the extent to which a
control input must be manipulated to achieve a desired mode of
operation. The method may then proceed to step 116.
[0060] At step 116, the method may determine the probable effects
to plant operation of each of the available control inputs/variance
amounts from step 114. It will be appreciated that these types of
calculations may be achieved per conventional power plant control
programs and modeling software, such as those systems and methods
mention herein and others similar to them. It further will be
appreciated that these calculations may involve an iterative
process that takes into account efficient control
measures/counter-measures which may be made in response to the
proposed variance of the relevant control input, economic
considerations, wear and tear to the power plant, operator
preferences, plant operational boundaries, etc. The method then may
proceed to Step 118.
[0061] Plant operation boundaries may include any prescribed limit
that must be followed so that efficient operation is achieved
and/or undue wear and tear or more serious damage to systems is
avoided. For example, operational boundaries may include maximum
allowable temperatures within the turbines 30, 32 or combustor
components. It will be appreciated that exceeding these
temperatures may cause damage to turbine components or cause
increased emissions levels. Another operational boundary includes a
maximum compressor pressure ratio across each of the oxidant
compressor 11 and the recirculation compressor 12. Exceeding this
limitation may cause the unit to surge, which may cause extensive
damage to components. Further, the turbine may have a maximum mach
number, which indicates the maximum flow rate of the combusted
gases at the exit of the turbine. Exceeding this maximum flow rate
may damage turbine components. Given the possible configuration of
combustors within the power plant 9, relative pressures of the
flows delivered at the combustors 22, 24 by each of the compressors
11, 12 may be another operational boundary. That is, depending on
the configuration of the combustor 22, 24 and the manner in which
flows are combined, the pressure of the compressed oxidant
delivered by the oxidant compressor 11 must be within a certain
range of that supplied by recirculation compressor 12 to avoid
aerodynamic losses, backflow, and other potential issues.
[0062] At step 118, the method may determine which of the available
control inputs/variance amounts from the above step is most
favorable or preferred. This determination, in large part, may be
based upon the effects to system operation that were calculated in
step 116 as well as the extent to which the control input/variance
amount is able to manipulate the power plant system toward the
intended mode of operation. Then, for whichever control
input/variance amount is deemed most favorable, the method may
determine if the proposed control input/variance amount should be
executed based on whether the associated benefits of achieving
stoichiometric point operation (which may include the benefits of
being able to extract working fluid) outweighs the costs associated
with executing the variance amount. It will be appreciated that
economic considerations and operator preferences may be included in
this determination. Based on this calculation, the method then may
execute the proposed control input/variance amount or not. The
method then may return to step 104, and an iterative process by
which stoichiometric point operation within one of the combustors
is ultimately achieved or determined not possible due to some
operational constraint.
[0063] It will be appreciated that there are many possible control
inputs/variance amounts that affect the stoichiometric ratio in the
combustors 22, 24. In preferred embodiments, one such control input
includes controllably varying the compressed oxidant amount
delivered to the combustors 22, 24. It will be appreciated that
controllably varying the supply of compressed oxidant may have a
significant effect on the stoichiometry ratio within the combustors
22, 24. For example, if sensors indicate that, given the supply of
fuel to a combustor, more compressed oxidant (i.e., more oxygen) is
needed to achieve stoichiometric combustion, the supply of
compressed oxidant may be increased by manipulating inlet guide
vanes of the oxidant compressor 11 and/or changing valve settings
on the oxidant valves 54, 68 so that more compressed oxidant is
able to pass through the oxidant conduit 52, 67 associated with the
combustor. On the other hand, varying fuel supply is another
control input that may be used to achieve operation at a preferred
stoichiometric ratio. In this case, for example, sensors 70 may
indicate that, given the compressed oxidant amount being delivered
to the combustor, more fuel is needed to achieve stoichiometric
point operation. The fuel amount being delivered to the one or both
combustors 22, 24 may be increased by manipulating one or both of
the fuel valves 58, 59. Further, it will be appreciated that
stoichiometric point combustion may be controlled in one of the
combustors by changing settings that are directly related to the
other combustor. This is because changed settings within one
combustor may create excess oxidant or unspent fuel in the
recirculation loop 10 that is ultimately ingested within the other
combustor, thereby affecting the combustion stoichiometric ratio
therein.
[0064] In one exemplary mode of control, the fuel/oxidant input
into the power plant 9 may be set such that there is excess oxidant
(i.e., a stoichiometric ratio greater than 1) in whichever of the
combustors 22, 24 is meant to operate at the stoichiometric point.
Then, the control process may decrease the excess oxidant by small
increments within the relevant combustor 22, 24 (either by
increasing fuel flow to the combustor or by decreasing the oxidant
supply) while monitoring the stoichiometric ratio therein by
measuring a relevant process variable. In certain embodiments, this
may continue until the stoichiometric ratio is within a preferred
range, while still being slightly above 1 (i.e., still having
excess oxidant). This may be implemented by slowly increasing
oxidant flow, decreasing fuel flow, or both to the particularly
combustor 22, 24, while monitoring stoichiometric conditions
therein. It may also be done indirectly by slowly increasing
oxidant flow, decreasing fuel flow, or both to the other combustor
22, 24 so that excess fuel or oxidant becomes part of the working
fluid and ingested into the relevant combustor.
[0065] FIGS. 8 and 9 provide schematic illustrations of alternative
configurations of exemplary power plants according to the present
application. As shown, these power plants also employ exhaust gas
recirculation and a reheat combustion system similar to those
described above. However, the power plants of FIGS. 8 and 9 provide
dual extraction locations on the recirculation loop. It will be
appreciated that while the description of components, system
configurations, and control methods provided above are applicable
to the power plants of FIGS. 8 and 9 (as well as some of the
functionality described below being applicable to the components,
system configuration, and control methods described above), the
dual extraction locations provide a novel application that enables
enhanced functionality, which may beneficially employed in certain
operating conditions. As before, the power plant 9 may include a
recirculation loop 10 about which a working fluid is recirculated.
The recirculation loop 10 may include a plurality of components
that are configured to accept an outflow of working fluid from a
neighboring upstream component and provide an inflow of working
fluid to a neighboring downstream component. The components of the
recirculation loop 10 may include: a recirculation compressor 12;
an upstream combustor 22 positioned downstream of the recirculation
compressor 12; a high-pressure turbine 30 positioned downstream of
the upstream combustor 22; a downstream combustor 24 positioned
downstream of the high-pressure turbine 30; a low-pressure turbine
32 positioned downstream of the downstream combustor 24; and
recirculation conduit 40 configured to complete the loop by
directing the outflow of working fluid from the low-pressure
turbine 32 to the recirculation compressor 12. As described in more
detail above in relation to the other exemplary power plants 9
provided in the several figures, the power plant 9 of FIGS. 8 and 9
may further include systems and components that control and deliver
a compressed oxidant amount to each of the upstream combustor and
the downstream combustor. As described above in relation to the
other exemplary power plants 9, the power plant 9 of FIGS. 8 and 9
may further include systems and components that control a fuel
amount supplied to each of the upstream combustor 22 and the
downstream combustor 24. The power plant 9, as illustrated, may
further include systems and components that extract the working
fluid exhausted from the upstream combustor 22 from a first
extraction point 75, and systems and components that extract the
working fluid exhausted from the downstream combustor 24 from a
second extraction point 76. The power plant 9, as illustrated in
FIGS. 8 and 9 and discussed further above, may include systems and
components for controlling operation such that each of the upstream
combustor 22 and the downstream combustor 24 periodically operate
at a preferred stoichiometric ratio, as well as means for
selectively extracting working fluid from the first extraction
point 75 and the second extraction point 76 based on which of the
upstream combustor 22 and the downstream combustor 24 operates at
the preferred stoichiometric ratio.
[0066] In certain embodiments, the first extraction point 75 may
include a first controllable extracted gas valve 61 for controlling
the amount of gas extracted at that location. The first extraction
point 75 may be disposed on the recirculation loop 10 between the
upstream combustor 22 and, proceeding in a downstream direction,
the downstream combustor 24. As illustrated in FIGS. 8 and 9, one
exemplary location for the first extraction point 75 is the aft end
of the high-pressure turbine 30. The first controllable extracted
gas valve 61 may be controllable to at least two settings: a closed
setting that prevents the extraction of working fluid and an open
setting that allows the extraction of working fluid. Similarly, the
second extraction point 76 may include a second controllable
extracted gas valve 61 for controlling the amount of gas extracted
at that location. The second extraction point 76 may be disposed on
the recirculation loop 10 between the downstream combustor 24 and,
proceeding in a downstream direction, the upstream combustor 22. As
illustrated in FIG. 8, one exemplary location for the second
extraction point 76 is the aft end of the low-pressure turbine 32.
As illustrated in FIG. 9, another exemplary location for the second
extraction point 76 is on the recirculation conduit 40 between the
cooler 44 and the blower 46. Depending on the required properties
of the extracted gas, other locations are possible. The second
controllable extracted gas valve 61 may be controllable to at least
two settings: a closed setting that prevents the extraction of
working fluid and an open setting that allows the extraction of
working fluid.
[0067] In certain embodiments, the systems and components for
controlling the compressed oxidant amount supplied to the upstream
combustor 22 may include an oxidant compressor 11, a first oxidant
conduit 52 that is configured to direct compressed oxidant derived
from the oxidant compressor 11 to the upstream combustor 22, and a
first controllable oxidant valve 54 disposed on the first oxidant
conduit 52 that is controllable to at least three settings: a
closed setting that prevents delivery of the compressed oxidant to
the upstream combustor 22 and two open settings that allow delivery
of differing compressed oxidant amounts to the upstream combustor
22. In certain embodiments, the systems and components for
controlling the compressed oxidant amount supplied to the
downstream combustor 24 may include the oxidant compressor 11, a
second oxidant conduit 67 that is configured to direct compressed
oxidant derived from the oxidant compressor 11 to the downstream
combustor 24, and a second controllable oxidant valve 68 disposed
on the second oxidant conduit 67 that is controllable to at least
three settings: a closed setting that prevents delivery of the
compressed oxidant to the downstream combustor 24 and two open
settings that allow delivery of differing compressed oxidant
amounts to the downstream combustor 24. In certain embodiments, a
booster compressor 16 may be included that is disposed on at least
one of the first oxidant conduit 52 and the second oxidant conduit
67 (an example of which is shown in FIG. 6). The booster compressor
16 may be configured to boost the pressure of the compressed
oxidant flowing through at least one of the first 52 and the second
oxidant conduit 67 such that the compressed oxidant amount supplied
to at least one of the upstream 22 and the downstream combustor 24
comprises a pressure level that corresponds to a preferable
injection pressure of whichever of the upstream 22 and downstream
combustor 24. In certain embodiments, at an upstream end, the first
oxidant conduit 52 may include a first oxidant extraction location
81 at which the compressed oxidant is extracted from the oxidant
compressor 11. At an upstream end, the second oxidant conduit 67
may include a second oxidant extraction location 83 at which the
compressed oxidant is extracted from the oxidant compressor 11.
Within the oxidant compressor 11, the first oxidant extraction
location 81 may include a downstream position relative to the
second oxidant extraction location 83. The first oxidant extraction
location 81 may include a predetermined position within the oxidant
compressor 11 that corresponds to a preferable injection pressure
at the upstream combustor 22. The second extraction location 83 may
include a predetermined position within the oxidant compressor 11
that corresponds to a preferable injection pressure at the
downstream combustor 24.
[0068] In certain embodiments, the systems and components for
controlling the fuel amount supplied to the upstream combustor 22
may include an upstream combustor fuel supply 78 that may include a
controllable upstream combustor fuel valve or first controllable
fuel valve 58. The first controllable fuel valve 58 may be
controllable to at least three settings: a closed setting that
prevents delivery of fuel to the upstream combustor 22 and two open
settings that allow delivery of differing fuel amounts to the
upstream combustor 22. The systems and components for controlling
the fuel amount supplied to the downstream combustor 24 may include
a downstream combustor fuel supply 79 that may include a
controllable downstream combustor fuel valve or second controllable
fuel valve 59. The second controllable fuel valve 59 may be
controllable to at least three settings: a closed setting that
prevents delivery of fuel to the downstream combustor 24 and two
open settings that allow delivery of differing fuel amounts to the
downstream combustor 24. In certain embodiments, as shown in FIG.
8, the upstream combustor fuel supply 78 and the downstream
combustor fuel supply 79 may have a common source and, thus, a
common fuel type. In other embodiments, as shown in FIG. 9, the
upstream combustor fuel supply 78 and the downstream combustor fuel
supply 79 may have difference sources and may supply differing fuel
types.
[0069] As describe above in more detail, the power plant 9 of FIGS.
8 and 9 may include systems and components for controlling the
power plant 9 such that each of the upstream combustor 22 and the
downstream combustor 24 periodically operate at the preferred
stoichiometric ratio. In certain embodiments includes a
computerized control unit 65 that is configured to control the
settings of the first and second controllable oxidant valves 54 and
the first and second controllable fuel valves 58, 59.
[0070] As described in more detail above, in certain embodiments,
the power plant 9 of FIGS. 8 and 9 may include systems and
components for determining a current stoichiometric ratio at which
the upstream combustor 22 and the downstream combustor 24 operate.
In certain exemplary embodiments, the systems and components for
determining the current stoichiometric ratio at which the upstream
combustor 22 and the downstream combustor 24 operate include:
systems and components for measuring the compressed oxidant amount
being supplied to the upstream and downstream combustors 22, 24 and
systems and components for measuring the fuel amount being supplied
to the upstream and downstream combustors 22, 24; and systems and
components for calculating the current stoichiometric ratio at
which each of the upstream combustor 22 and the downstream
combustor 24 operates based on the measured compressed oxidant
amounts and the measured fuel amount being supplied to each. In
certain exemplary embodiments, the systems and components for
determining the stoichiometric ratio at which the upstream
combustor 22 and the downstream combustor 24 operate include: a
first testing component for testing the working fluid exhausted
from the upstream combustor 22; and a second testing component for
testing the working fluid exhausted from the downstream combustor
24. The first testing component and the second testing component
each may include one of a sensor for detecting excess oxidant and a
sensor for detecting unspent fuel. One or more CO sensors and one
or more humidity sensors may also be used, as one of ordinary skill
in the art will appreciate. The first testing location may include
a location within a range of positions on the recirculation loop
10. The range of positions may be defined between the first
extraction point 75 and, proceeding in an upstream direction, the
upstream combustor 22. The second testing location may include a
location within a range of positions on the recirculation loop 10.
The range of positions may be defined between the second extraction
point 76 and, proceeding in an upstream direction, the downstream
combustor 24.
[0071] In certain embodiments, the systems and components for
selectively extracting from the first extraction point 75 and the
second extraction point 76 based on which of the upstream combustor
22 and the downstream combustor 24 is being operated at the
preferred stoichiometric ratio includes a computerized control unit
65. In one preferred embodiment, the control unit 65 is configured
to: extract working fluid from the first extraction point 75 during
periods when the upstream combustor 22 operates at the preferred
stoichiometric ratio; and extract working fluid from the second
extraction point 76 during periods when the downstream combustor 24
operates at the preferred stoichiometric ratio.
[0072] As provided herein, the power plant of FIGS. 8 and 9 may be
operated per novel control methods. In certain embodiments, such
methods may include the steps of: recirculating at least a portion
of the working fluid through the recirculation loop 10; controlling
a compressed oxidant amount supplied to each of the upstream
combustor 22 and the downstream combustor 24; controlling a fuel
amount supplied to each of the upstream combustor 22 and the
downstream combustor 24; controlling the power plant 9 such that
each of the upstream combustor 22 and the downstream combustor 24
periodically operates at a preferred stoichiometric ratio; and
selectively extracting the working fluid from a first extraction
point 75 associated with the upstream combustor 22 and a second
extraction point 76 associated with the downstream combustor 24
based upon which of the upstream 22 and the downstream combustor 24
operates at the preferred stoichiometric ratio. The step of
selectively extracting the working fluid from the first 75 and the
second extraction points 76 may include selecting to extract from
the first extraction point 75 only during periods when the upstream
combustor 22 operates at the preferred stoichiometric ratio, and
selecting to extract working fluid from the second extraction point
76 only during periods when the downstream combustor 24 operates at
the preferred stoichiometric ratio. In one preferred embodiment,
for example, the upstream combustor 22 may be operated at the
preferred stoichiometric ratio during low-load operation, and the
downstream combustor 24 may be operated at the preferred
stoichiometric ration during full operation. The step of
selectively extracting working fluid from the first 75 and second
extraction points 76 may include controlling the settings of the
first 61 and second controllable extracted gas valves 61. The step
of controlling the compressed oxidant amount supplied to each of
the upstream and downstream combustors 22, 24 may include
manipulating the settings of the first and second controllable
oxidant valves 54, 68. The step of controlling the fuel amounts
supplied to each of the upstream and downstream combustors 22, 24
may include the steps of manipulating the settings of the first and
second controllable fuel valves 58, 59.
[0073] The step of controlling the power plant 9 such that each of
the upstream combustor 22 and the downstream combustor 24
periodically operate at the preferred stoichiometric ratio may
include using a computerized control unit 65 that is configured to
control the settings of the first and second controllable oxidant
valves 54 and the first 58 and second controllable fuel values 59.
The preferred stoichiometric ratio may include a stoichiometric
ratio of about 1, though the other ranges discussed herein are also
possible.
[0074] In certain embodiments, the method may include the steps of:
measuring a plurality of process variables of the power plant 9;
determining an output requirement for the power plant 9; based on
the measured process variables and the output requirement,
determining a desired mode of operation for the power plant 9;
determining a preferred stoichiometric combustor, the preferred
stoichiometric combustor including whichever of the upstream
combustor 22 and the downstream combustor 24 is preferred for
operation at the preferred stoichiometric ratio given the desired
mode of operation for the power plant 9 and a chosen criteria; and
controlling the power plant 9 such that the preferred
stoichiometric combustor operates at the preferred stoichiometric
ratio. It will be appreciated that power plants configured as with
dual combustion systems may choose to shut-down one of the
combustion systems during a turndown mode of operation, thereby
more efficiently satisfying a lower output requirement.
Accordingly, in certain embodiments, the desired mode of operation
includes a turndown mode of operation during which only one of the
upstream combustor 22 and the downstream combustor 24 operates. In
this case, the preferred stoichiometric combustor may include
whichever of the upstream combustor 22 and the downstream combustor
24 operates during the turndown mode of operation. In certain
embodiments, the upstream combustor 22 is the combustor that
operates during the turndown mode of operation.
[0075] The chosen criteria for determining the preferred
stoichiometric combustor may be any of several. In certain
preferred embodiments, the chosen criteria relates to the
efficiency level of the power plant 9. In this manner, the
preferred stoichiometric combustor is the combustor that, when
operated at the preferred stoichiometric ratio, promotes
efficiency. The chosen criteria also may be related to economic
considerations, i.e., the preferred stoichiometric combustor is the
one that promotes the profits of the power plant 9.
[0076] In certain embodiments, the method of the present
application may further include the steps of: determining a current
stoichiometric ratio at which the preferred stoichiometric
combustor operates; determining whether the current stoichiometric
ratio is equal to the preferred stoichiometric ratio; and
extracting working fluid from the extraction point associated with
the preferred stoichiometric combustor if the current
stoichiometric ratio is determined to be equal to the preferred
stoichiometric ratio. In certain embodiments, this may include the
steps of: measuring the compressed oxidant amount being supplied to
the upstream and downstream combustors 22, 24; measuring the fuel
amount being supplied to the upstream and downstream combustors 22,
24; and calculating the current stoichiometric ratio at which the
preferred stoichiometric combustor operates based on the measured
compressed oxidant amount being supplied to the upstream and
downstream combustors 22, 24 and the measured fuel amounts being
supplied to the upstream and downstream combustors 22, 24. In
certain embodiments, the step of determining the current
stoichiometric ratio at which the preferred stoichiometric
combustor operates includes the steps of: if the upstream combustor
22 may include the preferred stoichiometric combustor, testing the
working fluid exhausted from the upstream combustor 22; and if the
downstream combustor 24 may include the preferred stoichiometric
combustor, testing the working fluid exhausted from the downstream
combustor 24. The working fluid exhausted from the upstream
combustor 22 may be tested at a first test location by one of a
sensor for detecting excess oxidant and a sensor for detecting
unspent fuel. The first test location may include a location within
a range of locations on the recirculation loop defined between the
first extraction point 75 and, proceeding in an upstream direction,
the upstream combustor 22. The working fluid exhausted from the
downstream combustor 24 may be tested at a second test location by
one of a sensor for detecting excess oxidant and a sensor for
detecting unspent fuel. The second test location may include a
location within a range of locations on the recirculation loop
defined between the second extraction point 76 and, proceeding in
an upstream direction, the downstream combustor 24. In this manner,
the status of the exhaust prior to extraction may be tested to
confirm desired properties.
[0077] In certain embodiments, the step of controlling the power
plant 9 such that the preferred stoichiometric combustor operates
at the preferred stoichiometric ratio includes the step of
operating a feedback loop control mechanism that includes
manipulating a control input of the power plant 9 based on the
measured plurality of the process variables. The methods of
operating a feedback loop control mechanism are discussed in more
detail above. In certain cases, it will be appreciated that the
step of measuring the plurality of process variables may include
measuring the compressed oxidant amount and the fuel amount
supplied to the preferred stoichiometric combustor and calculating
a current stoichiometric ratio in the preferred stoichiometric
combustor based on the measured compressed oxidant amount and fuel
amount supplied to the preferred stoichiometric combustor. In
certain embodiments, the control input may include the settings for
whichever of the first and second controllable oxidant valves 54,
68 correspond to the preferred stoichiometric combustor and
whichever of the first and second controllable fuel valves 58, 59
correspond to the preferred stoichiometric combustor.
[0078] In certain embodiments, the step of measuring the plurality
of process variables may include measuring the compressed oxidant
amounts and the compressed fuel amounts being supplied to each of
the upstream and downstream combustors 22, 24. The step of
calculating the current stoichiometric ratio in the preferred
stoichiometric combustor may include balancing, in each of the
upstream and downstream combustors 22, 24, the measured oxygen
amount against the measured fuel amount to determine whether the
preferred stoichiometric combustor ingests an excess fuel amount or
an excess oxidant amount that is present in the working fluid from
whichever of the upstream and downstream combustors 22, 24 is not
the preferred stoichiometric combustor.
[0079] In certain embodiments, the step of measuring the plurality
of process variables may include testing a working fluid content at
a position on the recirculation loop that is both downstream of the
preferred stoichiometric combustor and upstream of whichever of the
upstream and downstream combustors 22, 24 is not the preferred
stoichiometric combustor. The control input may include at least
one of the fuel amount supplied to the upstream combustor 22, the
fuel amount supplied to the downstream combustor 24, the compressed
oxidant amount supplied to the upstream combustor 22, and the
compressed oxidant amount supplied to the downstream combustor 24.
The step of testing the working fluid content may include measuring
at least one of an oxidant content and an unspent fuel content of
the working fluid, which may further include the step of
calculating a current stoichiometric ratio in the preferred
stoichiometric combustor based on the testing of the working fluid
content.
[0080] In certain exemplary embodiments, the method of the present
application includes controlling the power plant 9 such that both
of the upstream combustor 22 and the downstream combustor 24
periodically operate at the preferred stoichiometric ratio during
the same period of time. In this case, selectively extracting the
working fluid from the first extraction point 75 and the second
extraction point 76 may include extracting working fluid from both
the first extraction point 75 and the second extraction point 76
when both combustors 22, 24 operate at the preferred stoichiometric
ratio. As shown in FIGS. 8 and 9, the two extracted gas flows may
be combined at a combining point 86. That is, the method of the
present application may include the step of combining the working
fluid extracted from the first extraction point 75 and the working
fluid extracted from the second extraction point 76. The method may
further include the step of controllably combining the two
extracted flows of working fluid such that a combined flow of
extracted working fluid includes a desired characteristic. It will
be appreciated that this may be done by controlling the settings of
the controllable extracted gas valves 61 that are included at each
extraction point 75, 76. Depending on the downstream applications
for which the extracted gas is extracted, it is beneficial to have
the ability to provide the extracted gas at varying pressure levels
or temperatures. This may be achieved by mixing the gases extracted
from different points on the recirculation loop 10 in desired or
controlled amounts. As shown in FIG. 9, the first extraction point
75 extracts gas from a region of relative high temperature and high
pressure, while the second extraction point 76 extracts gas from a
region of relatively low temperature and low pressure. It will be
appreciated that by mixing the two flows in a controlled manner,
desired extracted gas characteristics within the range of
characteristics defined by the differing extraction location may be
achieved.
[0081] Turning now to FIGS. 10-13, schematic drawings illustrating
configurations of alternative power plants that employ exhaust gas
recirculation and a single combustion system are provided. It will
be appreciated that the power plant 9 of these figures includes
many of the same components as the power plants described above and
that these components may be employed in much the same manner at
that described elsewhere in this application. As stated, any of the
descriptions pertaining to any of the power plants that one of
ordinary skill in the art would appreciate as not being limited to
a specific configuration is applicable to all the configurations,
particularly as such alternatives may be described in the claims or
any amendments made thereto. In certain embodiments, the power
plant 9 is configured to include a recirculation loop 10 about
which a working fluid is recirculated. As before, the recirculation
loop 10 may include a plurality of components configured to accept
an outflow of working fluid from a neighboring upstream component
and provide an inflow of working fluid to a neighboring downstream
component. In this case, the recirculation loop 10 includes a
recirculation compressor 12; a combustor 22 positioned downstream
of the recirculation compressor 12; a turbine 30 positioned
downstream of the combustor 22; and a recirculation conduit 40
configured to direct the outflow of working fluid from the turbine
30 to the recirculation compressor 12. The power plant 9 is
configured to have a single combustion system. As such, the
recirculation loop 10 may be configured to prevent the input of
combustion gases at all locations except for an input related to
the combustor 22. As shown, the power plant 9 may further include a
first extraction point 75 and a second extraction point 76
positioned on the recirculation loop 10. The outflow of working
fluid from the turbine 30 includes exhaust gases, which, via the
recirculation conduit 40, are directed to the recirculation
compressor 12. The recirculation compressor 12 is configured to
compress the exhaust gases such that the outflow of working fluid
from the recirculation compressor 12 includes compressed exhaust
gases;
[0082] The first extraction point 75 may include a controllable
extraction valve 61 that is controllable to at least two settings:
a closed setting that prevents the extraction of working fluid and
an open setting that allows the extraction of working fluid. The
second extraction point 76 may include a controllable extraction
valve 61 that is controllable to at least two settings: a closed
setting that prevents the extraction of working fluid and an open
setting that allows the extraction of working fluid.
[0083] The power plant 9 may be operated or controlled such that
the combustor 22 at least periodically operates at a preferred
stoichiometric ratio. The preferred stoichiometric ratios may be
similar to those ratios discussed above. To achieve this type of
operation, a compressed oxidant amount and a fuel amount supplied
the combustor 22 may be controlled. The compressed oxidant amount
may be controlled by an oxidant compressor 11, an oxidant conduit
52 that is configured to direct compressed oxidant derived from the
oxidant compressor 11 to the combustor 22, and a controllable
oxidant valve 54 disposed on the oxidant conduit that is
controllable to at least two open settings that allow delivery of
differing compressed oxidant amounts to the combustor 22. The fuel
amount may be controlled by a controllable fuel valve 58 that has
at least two open settings that allow delivery of differing fuel
amounts to the combustor 22. It will be appreciated that the power
plant 9 may be controlled such that the combustor 22 at least
periodically operates at the preferred stoichiometric ratio via a
computerized control unit 65 that is configured to control the
settings of the controllable oxidant valve 54 and the controllable
fuel valve 58, and may include systems for determining a current
stoichiometric ratio at which the combustor 22 operates, the
various systems for which are discussed in detail above, whether
the current stoichiometric ratio is equal to the preferred
stoichiometric ratio, as well as a control feedback loop mechanism
that achieves the desired modes of operations. As discussed in more
detail below, the computerized control unit 65 may be configured to
selectively extract working fluid from at least one of the first
extraction point 75 and the second extraction point 76 based on
whether the current stoichiometric ratio in the combustor 22 is
determined to be equal to the preferred stoichiometric ratio, as
well as the intended downstream uses of the extracted working
fluid.
[0084] In certain embodiments, the power plant 9 includes a
recirculation conduit 40 that is configured to collect exhaust
gases from the turbine 30 and direct the exhaust gases to an intake
of the recirculation compressor 12. The recirculation conduit 40
may further include a heat recovery steam generator, the heat
recovery steam generator including a boiler, the heat recovery
steam generator being configured such that the exhaust gases from
the turbine 30 includes a heat source for the boiler. The
recirculation conduit 40 may include a chiller 44 and a blower 46
positioned thereon. The chiller 44 may be configured to
controllably remove an amount of heat from the exhaust gases
flowing through the recirculation conduit 40 such that a more
desirable temperature is achieved at the intake of the
recirculation compressor 12. The blower 46 may be configured to
controllably circulate the exhaust gases flowing through the
recirculation conduit 40 such that a more desirable pressure is
achieved at the intake of the recirculation compressor 12.
[0085] The power plant 9 may include instruments, sensors, and
systems for determining a property of characteristic of the working
fluid at the extraction points 75, 76. These may include direct
measurement of the characteristic or calculation based on other
measured process variables. The characteristic may include any
property of the working fluid, such as, pressure and temperature.
As stated, the extracted working fluid has economic value in
certain industrial and other applications. It will be appreciated
that if the extracted working fluid may be efficiently delivered
with desired characteristics given an intended application, such as
at a desired pressure or temperature, the value of it is increased.
In certain embodiments, the means for determining the
characteristic of the working fluid at the first extraction point
75 and the second extraction point 76 may include a pressure sensor
and/or a temperature sensor. The computerized control unit 65 may
be configured to selectively extract the working fluid from only or
just the first extraction point 75, just the second extraction
point 76, or both the first and second extraction point 75, 76
based on the characteristic of the working fluid that is determined
to be at each of the extraction points 75, 76. The computerized
control unit 65 may do this via controlling the settings of the
first and second controllable extraction valves 61.
[0086] The computerized control unit 65 may be configured to
determine a preferred value for the characteristic of the working
fluid. This may be done via determining an intended downstream
application for the extracted working fluid, which could be
completed via consulting an operator entered value or otherwise.
The system then could determine a preferred value for the
characteristic of the working fluid based on what would be a
preferred value given the intended downstream application.
[0087] The extraction points 75, 76 may include various locations.
While a few preferred embodiments relating to extraction point
configuration are provided in FIGS. 10-13, it will be appreciated
that others are possible. As shown in FIG. 10, the first extraction
point 75 may have a location within the recirculation compressor
12, and the second extraction point 76 may have a location within
the turbine 30. As shown in FIG. 11, the first extraction point 75
may have a location within the recirculation compressor 12, and the
second extraction point 76 may have a location within the
recirculation conduit 40. As shown in FIG. 12, the first extraction
point 75 may have a first location within the recirculation
compressor 12, and the second extraction point 76 may have a second
location within the recirculation compressor 12. As shown in FIG.
13, the first extraction point 75 may have a first location within
the turbine 30, and the second extraction point 76 may have a
second location within the turbine 30. The advantages of these
configurations are discussed in more detail below.
[0088] The present application further describes a method of
controlling a power plant that includes configurations discussed
above in relation to FIGS. 10-13. In general, these methods may
include the steps of: recirculating at least a portion of the
working fluid through the recirculation loop; controlling the power
plant such that the combustor 22 at least periodically operates at
a preferred stoichiometric ratio; and extracting working fluid from
at least one of a first extraction point 75 and a second extraction
point 76 positioned on the recirculation loop 10 during the periods
when the combustor 22 operates at the preferred stoichiometric
ratio. The step of controlling the power plant such that the
combustor 22 periodically operates at the preferred stoichiometric
ratio may include the steps of controlling a compressed oxidant
amount and a fuel amount supplied to the combustor 22.
[0089] The method may further include the steps of: determining a
characteristic of the working fluid at the first extraction point
75; determining a characteristic of the working fluid at the second
extraction point 76; and, based on the characteristic of the
working fluid at the first and second extraction points 75,76
selectively extracting the working fluid from just the first
extraction point 75, just the second extraction point 76, or both
the first and second extraction points 75, 76. Based on a
downstream application, the method may determine a preferred value
for the characteristic of the working fluid, which may also be used
to selectively extract working fluid from the extraction points 75,
76. This type of method of operation may result in working fluid
being extracted from both the first extraction point 75 and the
second extraction point 76 at the same time. In this instance, the
method may controllably mix the extracted flows of working fluid
from both extraction points 75, 76 so as to create a combined flow
of extracted working fluid that has a characteristic consistent
with the preferred value for the characteristic. As before, the
preferred value for the characteristic of the working fluid may be
based on an intended downstream application. A computerized control
unit 65 may be configured to control the settings of the various
valves and other components discussed herein so that the desired
modes of operation are achieved.
[0090] In certain embodiments, the step of selectively extracting
the working fluid from just the first extraction point 75, just the
second extraction point 76, or both the first and second extraction
points 75, 76 includes the steps of: when the characteristic of the
working fluid at the first extraction point 75 is within a
predetermined range relative to the preferred value for the
characteristic, extracting from just the first extraction point 75;
when the characteristic of the working fluid at the second
extraction point 76 is within a predetermined range relative to the
preferred value for the characteristic, extracting from just the
second extraction point 76; when the preferred value for the
characteristic is within a predetermined range nested between the
characteristic of the working fluid at the first extraction point
75 and the characteristic of the working fluid at the second
extraction point 76, and extracting from both the first and second
extraction points 75, 76. In this manner, the method may employ
just one extraction point when the desired characteristic may be
achieved this way, or extract from both extraction points when
mixing may be employed to deliver the extracted gases in a more
desirable state given a downstream application. In certain
embodiments, these steps may include the following: when the
characteristic of the working fluid at the first extraction point
75 is approximately equal to the preferred value for the
characteristic, extracting from the first extraction point 75; when
the characteristic of the working fluid at the second extraction
point 76 is approximately equal to the preferred value for the
characteristic, extracting from the second extraction point 76; and
when the preferred value for the characteristic falls in between
the characteristic of the working fluid at the first extraction
point 75 and the characteristic of the working fluid at the second
extraction point 76, extracting from both the first and second
extraction points 75, 76. When the method operates to extract
working fluid from both extraction points 75, 76, a mixing step, as
mentioned, may be employed to create a combined flow that is more
desirable. In certain embodiments, this may be achieved by
controlling the setting of the first controllable extraction valve
61 such that a first predetermined amount of working fluid is
extracted from the first extraction point 75; controlling the
setting of the second controllable extraction valve 61 such that a
second predetermined amount of working fluid is extracted from the
second extraction point 76; and combining the first predetermined
amount of working fluid with the second predetermined amount of
working fluid at a combining junction such that the combined flow
of extracted working fluid is formed. It will be appreciated that,
given the characteristic of the working fluid at the first
extraction point 75 and the second extraction point 76, the first
predetermined amount of working fluid extracted from the first
extraction point 75 and the second predetermined amount of working
fluid extracted from the second extraction point 76 may include
predetermined amounts of working fluid that, once mixed, result in
the combined flow of extracted working fluid having the preferred
value for the characteristic. As stated, the characteristic may be
one of pressure and temperature, though others are possible.
[0091] The extraction point locations may be predetermined to
provide desired operation, efficiency, and flexibility in
delivering extracted flows having desired characteristics.
Generally, the first extraction point 75 may have a predetermined
first location within the recirculation loop 10 and the second
extraction point 76 may have a predetermined second location within
the recirculation loop 10. In one preferred embodiments, the first
predetermined location within the recirculation loop 10 and the
second predetermined location within the recirculation loop 10 are
selected such that the working fluid at each include a dissimilar
first characteristic and a similar second characteristic. In this
case, the working fluid extracted from the first extraction point
75 and the second extraction point 76 may be mixed to achieve a
wide range of levels for the first characteristic, while the mixing
has little effect on the resulting second characteristic, which
will remain at about the level of the similar second
characteristics of the extracted flows. In other cases, the first
predetermined location within the recirculation loop 10 and the
second predetermined location within the recirculation loop 10 may
be selected such that the working fluid at each includes a
dissimilar first characteristic and a dissimilar second
characteristic. This time, the working fluid extracted from the
first extraction point 75 and the second extraction point 76 may be
mixed to achieve a wide range of first characteristic values and a
wide range of second characteristic values.
[0092] Referring to FIG. 10, it will be appreciated that the
position within the recirculation compressor 12 for the first
extraction point 75 and the location within the turbine 30 for the
second extraction point 76 may be selected such that the dissimilar
first characteristic is pressure and the similar second
characteristic is temperature. Referring to FIG. 11, it will be
appreciated that the position within the recirculation compressor
12 for the first extraction point 75 and the location within the
recirculation conduit 40 for the second extraction point 76 may be
selected such that the dissimilar first characteristic is pressure
and the similar second characteristic is temperature. The location
for the second extraction point 76 may be varied to produce other
results, such as producing a dissimilar temperature characteristic.
Another possible configuration includes positioning first
extraction point 75 in the turbine 30 and the second extraction
point 76 in the recirculation conduit 40 so that dissimilar
pressure and dissimilar temperature characteristics at the two
extraction locations are achieved. It will be appreciated that this
type of arrangement may provide great flexibility in the mixing of
extracted flows to achieve a broad range of values for each of the
pressure and temperatures characteristics.
[0093] In another embodiment, as illustrated in FIG. 12, the first
extraction point 75 may have a first predetermined location within
the recirculation compressor 12, which may be selected to provide a
desired pressure or temperature level for the extracted working
fluid during an anticipated first mode of operation for the power
plant 9. The second extraction point 76 may have a second
predetermined location within the recirculation compressor 12,
which may be selected to provide the desired pressure or
temperature level for extracted working fluid during an anticipated
second mode of operation for the power plant 9. It will be
appreciated that this configuration provides the flexibility of
extracting working fluid at a consistent pressure or temperature
level, i.e., the desired pressure or temperature level, no matter
if the power plant 9 is operating in the first or second mode of
operation. In a preferred embodiment, the modes coincide with a
base load mode of operation and a turndown mode of operation. It
will be appreciated that this configuration further provides the
advantageous alternative of extracting at different pressure or
temperature levels during those times when the operation mode of
the power plant 9 remains unchanged.
[0094] In another embodiment, as illustrated in FIG. 13, the first
extraction point 75 may have a first predetermined location within
the turbine 30, which may be selected to provide a desired pressure
or temperature level for extracted working fluid during an
anticipated first mode of operation for the power plant 9. The
second extraction point 76 may have a second predetermined location
within the turbine 30, which may be selected to provide the desired
pressure or temperature level for extracted working fluid during an
anticipated second mode of operation for the power plant 9. In this
case, it will be appreciated that the configuration provides the
flexibility of extracting working fluid at a consistent pressure or
temperature level, i.e., the desired pressure or temperature level,
no matter if the power plant 9 is operating in the first or second
mode of operation. In a preferred embodiment, the modes coincide
with a base load mode of operation and a turndown mode of
operation. It will be appreciated that this configuration further
provides the advantageous alternative of extracting at different
pressure or temperature levels during those times when the
operation mode of the power plant 9 remains unchanged.
[0095] From the above description of preferred embodiments of the
invention, those skilled in the art will perceive improvements,
changes and modifications. Such improvements, changes and
modifications within the skill of the art are intended to be
covered by the appended claims. Further, it should be apparent that
the foregoing relates only to the described embodiments of the
present application and that numerous changes and modifications may
be made herein without departing from the spirit and scope of the
application as defined by the following claims and the equivalents
thereof.
* * * * *